The AR-308® Receiver is designed to be stronger and lighter than anything on the market today. We invented the hybrid AR lower receiver and we used that experience in designing the AR-308. We have used our TN ARMS 15 lower in every caliber from .22 LR to 50 BMG. The AR-308 is 30% bigger and includes reinforcement in key areas. This lower receiver assembles just like an AR15 style lower. AR308 lpk is available here: http://www.tnarmsco.com/tn-arms-ar308-lower-part-kit/ with the roll pin (like an AR15) we use instead of a screw.